Field of the Invention
The invention relates to a light signal, in particular for rail-bound traffic routes, having a light source, an optical system and a control device for adjusting an emission characteristic.
In principle, light signals serve as signal emitters or symbol indicators which impart particular information by means of coloring and/or shaping of a luminous surface, that is, by means of the emission characteristic. This often involves safety-related information which must not be optically falsified or overlaid with extraneous light. The unwanted lighting up or falsification of a light point by the ingress of ambient light, for example sunlight or headlamp light is designated a phantom effect. By means of the phantom effect, in extreme cases, a false indication can occur due to an untimely illumination of a light point or a color shift. This effect is particularly disturbing when LED arrays are used as the light source, since LEDs can be stimulated to luminesce by incident light and in the case of LED light sources, rear reflectors are often used. Apart from the phantom generators which are predictable with projection, for example, a low sun for signals in an east-west orientation, sporadic or unforeseen sources also arise as phantoms, for example, vehicle or building lights, reflection at surfaces, for example, on glazed facades or snow coverings. Thus a signal which is intended to be phantom-proof by virtue of the location can be phantom-prone. In general, the attempt is made to minimize the phantom effect through shades, shields, the avoidance of east-west orientation or by the repetition of critical signals.
The explanations below relate essentially to light signals for representing signal indications for rail-bound traffic routes, but without the claimed subject matter being restricted to this use.
In the case of railway signals, it must be ensured that the traction vehicle driver can always unambiguously recognize the signal intended for him on approaching it. Herein, different route geometries, that is, straight stretches, curves and/or height differences must be taken into account. Apart from the far field representation, a near field representation of the signal indication is also required so that the traction vehicle driver can recognize the light signal even when standing directly in front of the signal. Furthermore, a brightness adjustment to different ambient light conditions, in particular a day/night adjustment, is required.
The light signals for rail-bound traffic routes are subject to strict regulation-related requirements with regard to the permitted brightness limits, the spatial light distribution and the phantom light strength.
FIG. 1 shows schematically the structure of a known light signal.
Herein, a housing 1 is provided, into which an LED light source 2 with secondary optics, for example, light guides or lenses, for light mixing and beam formation, as well as an optical system 3, are installed. The optical system 3 consists substantially of a front lens 4, at least one diffuser panel 5 and a front panel 6, wherein these components can also be configured as a combined part. A control device 7 is connected to a functional light sensor 8 within the housing 1 for detecting the intensity and/or color of the light flux. The control device 7 applies to the LED light source 2 the measurement values of the functional light sensor 8 and target parameters pre-set by a signal tower.
The diffuser panel 5 is preferably provided with a diffuser segment for the signal indication visualization in the near field, wherein a gray coloration of the diffuser panel 5 counteracts the phantom effect. With this uniting of the light scattering and the reduction of the phantom effect, however, a compromise unavoidably arises which leads thereto that the phantom protection effect is not sufficient at least for the group of light signals close to the ground which shine upwardly in the near field. Due to the dependence on scattering parameters pre-set at the signal tower, in order to achieve the optical power data, more gray filters and/or gray colored diffuser panels 5 are often required. The range of the transmissions of gray filters used extends from ca. 3% to over 70% transmittance. The necessary transmittance is created by the choice of the filter material and adjustment of the material thickness. Herein, the gray filter must adhere, apart from the mechanical installation conditions, also to the optical requirements regarding color neutrality and long term stability.